Imaging devices are used to produce machine-readable data which is representative of the image of an object, e.g. a page of printed text. One type of imaging device is a photoelectric imaging device. As used herein, the phrase "photoelectric imaging device" means any device which generates data representative of an imaged object through use of a photosensor array such as a charge coupled device (CCD). Photoelectric imaging devices include devices such as camcorders and digital cameras which instantaneously focus an entire image which is to be captured onto a two dimensional photosensor array. Photoelectric imaging devices also include line-focus systems.
Some line focus systems image an object by sequentially focusing narrow "scan line" portions of the object onto a linear photosensor array by sweeping a scanning head over the object. Such devices, commonly referred to as optical scanners include computer input devices usually referred to simply as "scanners" as well as facsimile machines and digital copy machines.
A line focus system is also used in some barcode readers. Generally, in line focus barcode readers, a narrow portion of a barcode is imaged onto a linear photosensor array. Electrical output from the photosensor array may then be analyzed to read the imaged barcode.
In a line-focus system, a light beam from an illuminated line object is imaged by a lens onto a linear photosensor array which is positioned remotely from the line object. The linear photosensor array is a single dimension array of photoelements which correspond to small area locations on the line object. These small area locations on the line object are commonly referred to as "picture elements" or "pixels." In response to light from its corresponding pixel location on the line object, each photosensor pixel element in the linear photosensor array (sometimes referred to simply as "pixels") produces a data signal which is representative of the light intensity that it experiences during an immediately preceding interval of time known as a sampling interval. All of the photoelement data signals are received and processed by an appropriate data processing system.
In a color optical scanner, a plurality of spectrally separated imaging beams (typically red, green and blue beams) must be projected onto a photosensor array or arrays. The construction and operation of color optical scanners is fully disclosed in the following United States patents: U.S. Pat. No. 4,870,268 of Vincent et al. for COLOR COMBINER AND SEPARATOR AND IMPLEMENTATIONS; U.S. Pat. No. 4,926,041 of Boyd for OPTICAL SCANNER (and corresponding EPO patent application no. 90306876.5 filed Jun. 22, 1990); U.S. Pat. No. 5,019,703 of Boyd et al. for OPTICAL SCANNER WITH MIRROR MOUNTED OCCLUDING APERTURE OR FILTER (and corresponding EPO patent application no. 90312893.2 filed Nov. 27, 1990); U.S. Pat. No. 5,032,004 of Steinle for BEAM SPLITTER APPARATUS WITH ADJUSTABLE IMAGE FOCUS AND REGISTRATION (and corresponding EPO patent application no. 91304185.1 filed May 9, 1991); U.S. Pat. No. 5,044,727 of Steinle for BEAM SPLITTER/COMBINER APPARATUS (and corresponding EPO patent application no. 91303860.3 filed Apr. 29, 1991); U.S. Pat. No. 5,040,872 of Steinle for BEAM SPLITTER/COMBINER WITH PATH LENGTH COMPENSATOR (and corresponding EPO patent application no. 90124279.2 filed Dec. 14, 1990 which has been abandoned); U.S. Pat. No. 5,227,620 of Elder, Jr. et al. for APPARATUS FOR ASSEMBLING COMPONENTS OF COLOR OPTICAL SCANNERS (and corresponding EPO patent application no. 91304403.8 file May 16, 1991) and U.S. Pat. No. 5,410,347 of Steinle et al. for COLOR OPTICAL SCANNER WITH IMAGE REGISTRATION HOLDING ASSEMBLY, which are all hereby specifically incorporated by reference for all that is disclosed therein.
In imaging devices and particularly the line-focus system described above, it is imperative for accurate imaging that the light beam from the object be accurately aligned with the photosensor array. In a typical line focus scanning device, before reaching the photosensor array, the imaging light beam is transmitted by one or more optical components, e.g., a lens. Even a slight misalignment between any of these optical components and the photosensor array can cause a serious mis-alignment between the beam and the photosensor array and result in a corresponding degradation in imaging quality.
Scanning devices that include light beam alignment features are fully described in U.S. Pat. No. 5,646,394 of Steinle et al. for IMAGING DEVICE WITH BEAM STEERING CAPABILITY and in U.S. patent application Ser. No. 09/121,793 filed on Jul. 23, 1998, of Christensen for PHOTOELECTRIC IMAGING METHOD AND APPARATUS, which are both hereby specifically incorporated by reference for all that is disclosed therein.
Typically, the optical components in an imaging device are mounted within an imaging device housing. The photosensor array is typically mounted to a circuit board, which, in turn, is mounted to the imaging device housing. It has been found, however, that it is difficult to accurately locate a photosensor array on its underlying circuit board. Thus, although the circuit board may be accurately aligned to the imaging device housing, the inaccuracy in location between the photosensor array and the circuit board often results in misalignment between the photosensor array and the remainder of the imaging device, e.g., the lens. As pointed out above, such misalignment can cause a serious mis-alignment between the beam and the photosensor array and result in a corresponding degradation in imaging quality.
To address this misalignment problem, it is conventional, when manufacturing an imaging device, to carefully align the photosensor array. This alignment procedure may be performed, for example, by placing the imaging device in a test fixture, imaging a test target with the imaging device and monitoring the output from photosensor array to determine the degree of misalignment of the photosensor array. Once the degree of misalignment has been determined, the photosensor array may be physically aligned with the remainder of the optical device, e.g., by moving the photosensor array circuit board relative to the remainder of the optical device housing. An example of an alignment procedure and mechanism used in a scanning device is fully disclosed in U.S. Pat. No. 4,753,908 of Christensen for PHOTOELECTRIC IMAGING DEVICE PHOTOSENSOR ARRAY ALIGNMENT APPARATUS AND METHOD, which is hereby specifically incorporated by reference for all that is disclosed therein.
Although the alignment procedure described above is generally effective in aligning a photosensor array, it is time consuming and generally labor intensive, thus adding to the complexity and cost involved in the manufacture of imaging devices.
Accordingly, it would be desirable to provide an optical imaging device which provides for accurate alignment between a photosensor array and the other optical components in the device.